1. Field of the Invention
The invention relates to a device for amplifying and sampling multiplexed analog signals, more particularly seismic signals. The device may be included in a seismic data acquisition chain for amplifying and sampling the signals supplied by one or more sensors disposed inside a seismic streamer, before digitization thereof by means of an analog-digital converter and recording thereof.
2. Description of the Prior Art
In a known process, the signals from a multiplexer disposed at the head are applied to a chain of amplifer elements disposed in series, the gain of each of them being fixed. A selection member chooses the number of amplification units which each signal must pass through taking into account its amplitude, so as to reach the optimum level and switch the output of the amplification unit where this is available, to the input of an analog-digital converter. The gains of the different stages may be all identical or else all different from each other, the gain of any stage being for example equal to the square of the value of the gain of the preceding stage. Such amplification chains are described for example in French Pat. Nos. 2.110.758 or 2.373.914.
The amplifiers formed of a cascade of amplification units comprising a multiplexer at the head have numerous drawbacks. They are relatively slow because the delays occuring in the different stages through which the signals pass are accumulative and are all the greater the higher the total gain to be applied thereto. The duration of the step for selecting the output where the signal presents optimum level compatible with the analog digital converter is all the greater the longer the chain.
Furthermore, storage of the values of the samples of signals available at the output of the head multiplexer is provided by a storage element of the sample and hold unit type whose defect is generally to create diaphony between successive samples, this being all the more sensitive the greater the dynamics of the signals which are applied thereto. The errors due to diaphony occuring before the amplifier are amplified by the whole chain of amplification stages.